In IEEE 802.11n/ac systems when double bandwidth was defined, half of the bandwidth was defined as primary channel and the other half as secondary channel. For example, a 40 MHz channel consists of primary 20 MHz and secondary 20 MHz channels. To enable coexistence of IEEE 802.11n/ac devices, standard specifications have defined Clear Channel Assessment (CCA) rules for both primary and secondary channels for the IEEE 802.11n/ac systems.